1. Chapter 1 Dipoles, molecular polarity

2. Ways to Represent Polarity in Molecules H F electron rich region electron poor region  

3. Dipole Moment (  ) H F electron rich region electron poor region    = q x r magnitude of charge =  = |  | bond length moment in Debyes (D) 1 D = 3.36 x 10 -30 Coulomb. meter

4. Explain the Trend  EN drops

5. More Complex Molecules? Consider molecular shape (bond orientation) bond polarity lone pairs (and sometimes) atom size What is symmetry of e- distribution?

6. Consider NH 3 Lewis Structure Need # valence e- from all atoms Need bond arrangement (connectivity)

7. Consider NH 3 Lewis Structure # valence e- = 5 (N) + 1 (3H) = 8e- Three N-H bonds H - N - H | H..

8. Consider NH 3 From the Lewis structure Deduce e- pair geometry at central atom THEN find molecular geometry/shape Any predictions? H - N - H | H..

9. : :: : Consider NH 3 molecular shape individual bond dipoles lone pair “dipoles” 4e- pairs at N  tetrahedral e- pr geometry Lone pair at N  molecular geometry/shape is trigonal pyramidal

10. .. : :: : Which molecule is more polar? molecular shape individual bond dipoles lone pair “dipoles”

11. .. : :: : Which molecule is more polar?

12. .. : :: : Which molecule is more polar?

13. Attractions Between Dipoles  

14. E coulomb  q E coulomb  1/d

15. Dipole-Dipole Interactions Dipoles align,  + of one dipole to   of another Magnitude of attraction E coulomb  (  + )(   )/d Increases with dipole moment ~5-25 kJ/mol   …... d d

16. NOFNOF H..…NOFNOF Hydrogen Bonding: Special Type of Dipole-Dipole Attraction From another molecule From one molecule  Only applies to molecules with H bonded to N, O, or F  ~10-40 kJ/mol (larger than most dipole-dipole attractions)  ..… H bond

17. Why Are Hydrogen Bonds So Strong?  EN for H and N,O, F = very large, so N-H, O-H, F-H bonds are very polar (  +  -  are large) H atoms are small, so N, O, F of one molecule can closely approach H of another molecule (d is small) NOFNOF H … NOFNOF E coulomb  (  + )(   )/d H bond

18. Hydrogen Bonds in Water

19. Large Molecules Can Have Intramolecular Hydrogen Bonds

20. Hydrogen Bonds in Chitin